DOOM / DOOM II  (classic, pre-source-port)
Type these during play. They work in the original DOS releases and in most
source ports (GZDoom, Chocolate Doom, Crispy Doom).

  IDDQD            God mode (degreelessness mode)
  IDKFA            All weapons, all keys, full ammo, 200% armour
  IDFA             All weapons and ammo, but NO keys
  IDCLIP           No clipping  (DOOM II)
  IDSPISPOPD       No clipping  (DOOM 1 only - yes, really)
  IDBEHOLDS        Berserk pack
  IDBEHOLDI        Invisibility (partial invisibility sphere)
  IDBEHOLDV        Invulnerability
  IDBEHOLDA        Computer area map
  IDBEHOLDL        Light amplification visor
  IDBEHOLDR        Radiation suit
  IDCHOPPERS       Chainsaw ("... doesn't suck - GM")
  IDMYPOS          Show current X/Y position and angle
  IDMUSxx          Play music track xx  (e.g. IDMUS08)
  IDCLEVxx         Warp to episode/level xx  (e.g. IDCLEV31 for a secret level)

NOTES
  - IDCLEV warps immediately and does NOT keep your inventory.
  - On Nightmare! difficulty IDDQD and IDKFA behave differently in some
    versions - originally they toggled rather than granted.
  - IDBEHOLD on its own brings up the sub-menu; the trailing letter picks.